US 8136485 B2
A flue offering reduced pluming is provided, the flue comprising a flue pipe for carrying flue gas and a liquid collector adapted to collect condensation from the interior of the flue pipe and to shield it from the flue gas.
1. A flue, comprising a flue pipe for carrying flue gas, and an elongate liquid collector within the flue pipe and extending along the flue pipe, and adapted to collect condensation from the interior of the flue pipe and to shield the condensation from the flue gas, and a liquid guide disposed within the flue pipe for directing droplets of moisture to flow towards the liquid collector in which the liquid guide is a helical guide that extends along the interior of the flue pipe, and in which the flue pipe is disposed within an air inlet pipe to a boiler such that the exterior of the flue pipe is cooled by air passing over it.
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18. A flue, comprising a flue pipe for carrying flue gas, the flue pipe having an elongate divider member extending along the flue pipe to partition the pipe into a gas carrying region and a liquid collection region shielded from the gas flow in the gas carrying region, and wherein apertures are provided in the divider member and/or between the divider member and the flue pipe to allow moisture to enter the elongate collection region.
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27. A flue, comprising a flue pipe for carrying flue gas, and an elongate liquid collector within the flue pipe and extending along the flue pipe, and adapted to collect condensation from the interior of the flue pipe and to shield the condensation from the flue gas, and a liquid guide disposed within the flue pipe for directing droplets of moisture to flow towards the liquid collector in which the liquid guide is a helical guide that extends along the interior of the flue pipe, and in which the helical guide is a helical depression within an interior wall of the flue.
The present invention relates to a flue, and more particularly although not exclusively to a flue for a domestic gas boiler.
Domestic dwellings are frequently fitted with balanced flue condensing gas boiler systems. In such an arrangement it is common for the boiler to be fitted on the interior face of an external wall of the building and a relatively short flue to be passed through the wall so as to vent outside. As a result, the flue tends to vent quite near to the ground, and often just at or slightly above head height.
A condensing boiler deliberately seeks to keep its flue gas temperature as low as reasonably possible. The flue gas naturally has to be warmer than the maximum water temperature required of the boiler, but any unnecessary increase above that results in heat being lost to the atmosphere and hence the efficiency of the boiler being reduced. Typically a condensing a boiler providing domestic heating can operate in its condensing mode and maintain a flue gas temperature below 58° C. However when operating in a hot water mode the boiler must seek to maintain its target temperature rise and flow rate and this causes the boiler to work in a less efficient regime where the flue gas temperature exceeds 58° C. and may reach 75° C.
A disadvantage of this move to lower flue gas temperatures is that the moisture within the flue gas formed as a by-product of the combustion process is far more likely to condense in the vicinity of the flue outlet. This can often be observed on windless days as the formation of a white cloud or plume around the flue vent. The formation of this plume is visually unattractive, especially in high density housing where several individual heating systems may vent in close proximity within, for example, a shared courtyard environment. Furthermore, as the moisture tends to concentrate other combustion products, such as acids, the formation of such low level plumes is undesirable from a public health stand point.
According to a first aspect of the present invention there is provided a flue, comprising flue pipe for carrying flue gas, and an elongate liquid collector within the flue pipe and adapted to collect condensation from the interior of the flue pipe and to shield it from the flue gas, and a liquid guide disposed within the flue pipe for directing droplets of moisture to flow towards the liquid collector.
It is thus possible to provide a modified flue in which condensate from the flue gas can be collected as the flue gas passes through the flue, and the condensate is then moved out of the path of the warm flue gas thereby inhibiting re-evaporation of the condensate back into the hot flue gas stream. This significantly reduces the amount of moisture contained within the flue gas as it exits the flue. This, in turn, reduces the instance and/severity of pluming.
Advantageously the flue pipe is cooled in order to enhance condensation. This is easily and conveniently achieved for a balanced flue boiler by placing the flue pipe within a fresh air inlet pipe such that, as a boiler fan draws fresh air into the boiler in order to promote the combustion process, the inrush of cool air from outside passes over the exterior surface of the flue pipe thereby cooling it.
Advantageously gas flow director means are provided in order to urge the hot flue gas to flow adjacent the wall of the flue pipe thereby encouraging it to give up thermal energy and the moisture contained therein to condense.
Advantageously the flow director means imparts rotational motion into the gas such that droplets of condensate are thrown towards the flue walls where they are collected.
Advantageously the interior surface of the flue is coated with a material that does not wet. A suitable material is PTFE.
One or more guides are formed in the vicinity of, or extend from, the flue walls in order to guide any moisture collecting on the walls towards the liquid collector. The guides may advantageously extend along the flue in helical manner with the pitch of the helix substantially matched to an average gas flow rate through the flue and the rotational rate imparted by the flow director such that the guides continue to urge the gas to maintain its rotational motion. The guide may be integrally formed as part of the flue pipe or may be an insert.
Advantageously a baffle plate is disposed along a lowermost portion of the flue pipe thereby shielding a portion of the flue pipe from the flue gases. The baffle may be perforated in order to allow moisture to pass through it. Alternatively, the interface between the baffle and the further flow director may provide apertures to allow moisture to pass from the gas flue pipe into the liquid collector.
According to a second aspect of the present invention there is provided a boiler having a flue according to a first aspect of the present invention.
The present invention will further be described, by way of example, with reference to the accompanying drawings, in which:
In the present invention a liquid collector is provided. This is formed by an interior baffle 12 which extends along the flue pipe in a lowermost region thereof in order to partition the flue pipe into a gas carrying region 14 and a liquid collection region 16 which is shielded from the gas flow by virtue of the baffle 12 and also by virtue of being closed, apart from a drain hole 28, to the gas inlet 4. The baffle 12 may be integrally formed with the flue pipe or, conveniently, may be an insert.
Water running down the side of the flue pipe 2 may pass around the edges of the baffle 12 or through perforations therein in order to enter the liquid collection region 16 where the liquid is now shielded from the flue gas flow and consequently does not become readmitted into the gas flow.
In order to enhance the formation of droplets within the flue pipe the interior surface of the flue pipe 2 is lined with (or alternatively the pipe may be made from) a material that does not wet. The concept of whether a surface wets or not depends upon the angle between the meniscus of a droplet of water sitting on that surface and the surface itself. If the angle of interception between the meniscus and the surface is greater than 90°, such that the edges of the droplet overhang the footprint of the droplet on the surface then the surface is said not to wet. Polytetrafluroethane represents a material which does not wet and consequently any moisture condensing on that surface quickly coalesces into droplets which run down the surface rather than sticking to it. The droplets run into the liquid collector formed by the region 16 thereby removing the liquid from the gas flow. As a further enhancement several fins 20, for example in the form of petal fins projecting from an interior surface of the flue pipe at the inlet region can be used to impart rotational motion on the gas as it passes through the flue pipe. This rotational motion tends to cause heavier particles within the gas, namely droplets of moisture, to be directed outwardly and onto the interior surface of the flue wall. This further enhances the liquid collecting properties of the flue pipe.
Advantageously further gas flow and liquid guide features are formed within the flue pipe. In the example shown in
The collected condensate tends to be acidic in nature and therefore it cannot merely be vented anywhere within the boiler. Boilers are already designed to cope with condensate collecting within the combustion chamber and therefore this feature can be taken advantage of in order to drain the collected condensate from the flue. To this end, the interior baffle 12 extends towards the flue inlet region 4 but closes against and seals with the wall of the flue pipe 2 so as to form a reservoir region 26. One or more drain apertures are formed within the baffle 12 in order to enable the condensate to drain into the combustion region of the boiler when the boiler is not in use. The apertures 28 are deliberately kept small in size so as to guard against any appreciable amount of gas flow occurring within the liquid collector when it is empty. As the collector starts to fill, the liquid flows towards the reservoir region 26 because the flue is installed slightly inclined from the horizontal. The gas pressure from the combustion region is just sufficient to hold the collected liquid within the reservoir whilst the boiler is operating. However, as soon as the combustion process stops and the flow of flue gases slows to a stop, the pressure then becomes insufficient and the collected liquid drains through the aperture 28 into the boiler from where it is collected by a boiler drain and disposed of.
It is thus possible to provide a simple and retrofitable modification to a flue for a boiler so as to reduce the instance of pluming.
It is thus possible to provide an improved flue which reduces the instance of pluming.